Variations in tissue perfusion have critically important consequences throughout medicine. This can be evident when not enough perfusion is available to keep tissues alive, when perfusion is restored to tissue after an acute event interrupting flow to that tissue, and when an additional source of blood flow, such as a bypass graft, is created to increase perfusion to the tissue supplied by a diseased vessel.
There are two general classifications of tissue perfusion variation, revascularization and devascularization.
Revascularization occurs when an intervention is performed to increase or restore blood flow to tissue, either by pharmacologic, catheter-based, or surgical interventions. The physiological benefit of successful revascularization is not only angiographic vessel patency, but in addition a demonstrable increase in tissue perfusion in the tissue supplied by flow within that vessel. In both circumstances, angiographic patency (vessel or graft) is one traditional marker of success. A more recently emerging consideration in the literature is the functional or physiologic success of revascularization, which is an index of the increase in perfusion to the tissue supplied by the vessel that was revascularized.
Devascularization is when tissue is deprived, either artificially or through a disease process, of enough blood flow and perfusion to compromise tissue viability. This can occur in a wide variety of surgical procedures, such as when tissue reconstruction flaps are created, or when a bowel tumor is removed and an anastomosis is performed. In these cases, maintenance of a normal threshold of perfusion to all parts of the tissue is critical to overall clinical procedural success, and to the avoidance of complications.
An example of revascularization that illustrates this principle is the setting of coronary artery bypass grafs (CABG). Here, where a stenotic area of narrowing in the vessel is bypassed, the increase in tissue perfusion results from a combination of flow down the bypass graft and the native vessel.
An example of devascularization that illustrates this principle is breast reconstruction after mastectomy, where removal of all or part of the breast is performed because of cancer. The remaining skin and underlying tissue needs to be stretched (“expanded”) to create a new breast; these skin and tissue edges can be devascularized in this process, resulting in wound breakdown and scar tissue formation.
In both these examples, the ability to directly assess perfusion at the time of surgery creates the opportunity to generate new, important information for decision-making. Examples include 1) measurement of the physiologic benefit of revascularization in CABG in a way quite distinctive and supplemental to angiographic graft patency alone; and 2) measurement leading to the avoidance of areas of tissue devascularization, which would decrease the incidence of complications from this surgical procedure.
Accordingly, there is a need for an analysis platform to intra-operatively visualize, display, analyze, and quantify angiography, perfusion, and the change in angiography and perfusion in real-time in tissues imaged by indocyanine green (ICG) near-infrared (NIR) fluorescence angiography technology (ICG-NIR-FA).